The present invention relates to a method and an apparatus for estimating or evaluating a position of a sound source in a structure being monitored. More particularly, the invention concerns a method and an apparatus which are advantageously suited to be used for detection of a position or location of a foreign or loose part within a structure such as, for example, a pressure vessel by estimating the position at which a sound is generated due to collision of the foreign or loose part with the structure.
According to a hitherto known method of estimating or evaluating a position of a sound source within a structure, such as a pressure vessel, peak value data and arrival time difference data derived from sound signals, originating from a number of known sound sources whose positions within the structure are previously known, are stored in the form of a file in a memory of a computer system, wherein comparison between patterns from the known sound sources and a pattern from a a position or location of an unknown sound generated by a foreign or loose part is arithmetically determined for each of the known sound sources, and the position of the known sound source which corresponds to the minimum or smallest difference is estimated to be the position or location of the unknown sound source, as is disclosed in U.S. Pat. No. 4,352,167. This known method is based on a pattern recognition procedure for comparing or correlating the data of the unknown sound source with the data of the known sound sources stored in the memory by making use of the fact that the pattern differences which are relied upon to indicate the distances from the known sound sources to the unknown sound source have significant correlations or proportional relations with the real or actual distances. However, in the case where the structure is not of a simply planar configuration, but has bends and openings in a complicated geometrical configuration as in most practical applications, difficulty is encountered in establishing a well defined proportional relation between the pattern difference and the actual or real distance. Consequently, even when the known sound source of which pattern difference from an unknown sound source is minimum can be retrieved from the file stored in the memory, there may arise a situation in which the real distance between the unknown sound source and the known sound source retrieved from the memory is not actually the shortest, resulting in an error in the estimation of the position of the unknown sound source with an appreciably high probability, which is a disadvantage. In order to improve the accuracy of estimation, it is required to increase the number of the known sound sources, which number is however limited in practical applications in view of the difficulty in providing the known sound sources due to the physical restriction imposed by the structure and a limitation in the capacity of the memory or storage.
The pattern difference is defined by a mathematical expression or model so as to have a predetermined correlation with a real distance. Such definition is discussed in the Shigeru Izumi's paper A22 titled "Estimation Of Sound Source Position In Pressure Vessel By Pattern Recognition Method" of a preparatory lecture collection for a session of the Japanese Atomic Energy Society held Sept. 20, 1982. It is reported that although there exists a reasonable correlation between the pattern difference and the real distance, significant deviations are nevertheless noted.